1. Field of the Invention
The present invention relates, in general, to a system and method for guaranteeing quality of service in networks and, more particularly, to a system and method for guaranteeing quality of service with respect to packets transmitted/received between a network capable of providing differentiated services and a home network.
2. Description of the Related Art
Generally, all conventional application programs in the Internet using Internet Protocol (IP) have provided only simple best-effort services. Further, a precedence sub-field and a TOS sub-field exist in a Type Of Service (TOS) region within an IPv4 header so as to provide services corresponding to respective IP datagrams. However, an Internet router providing only best-effort services does not use such sub-field information. Such a conventional Internet environment cannot satisfy various demands of Internet users any longer. Therefore, in order to satisfy the various service demands of Internet users, the provision of a guaranteed Quality of Service (QoS) in the Internet is needed.
Currently, in order to provide various services and guaranteed QoS, various research has been carried out all over the world. The Internet Engineering Task Force (IETF) has introduced various service models and mechanisms providing QoS in response to the demands of the Internet users. For remarkable mechanism of the introduced models, there are Integrated Services (IntServ) and Differentiated Services (DiffServ). The IntServ mechanism reserves end-to-end resources using Resource Reservation Protocol (RSVP) used to reserve resources, and provides QoS to users. However, since the RSVP reserves resources for respective flows, information and states required for resource reservation should be maintained for all flows, so that it is difficult to accommodate the RSVP in a large-scale network. That is, the RSVP is limited in flows, which can be managed by a system on a RSVP path. However, the DiffServ mechanism does not reserve resources for respective flows, but provides differentiated services to users in such a way that, if an edge node classifies data packets according to QoS required by users, a core node of the network differentially processes the classified data packets. Such a DiffServ mechanism improves the priority indication services of IPv4 defined in RFC791, and utilizes basic paradigm capable of providing various QoSs in the Internet using the defined services. Services can be the important characteristics of packet transmission, such as qualitative and statistic periods, throughput, delay, jitter and loss, in a set of one or more unidirectional paths within the network, or can be standardized by relative priorities to access network resources. The differentiation of services is required to allow differentiated prices of Internet services, satisfy various expectations of the users or accommodate different applications.
Services are provided to sets of traffic. For this purpose, a set of useful end-to-end services, which can be required by application programs using specific QoS, is defined in advance in the DiffServ. This set of services is called Per-Hop Behavior (PHB). PHB indicates that resources, such as buffers of routers or bandwidths, are allocated among competing traffic streams. Currently, IETF defines Expedited Forwarding (EF) PHB and Assured Forwarding (AF) PHB as newly differentiated forwarding schemes in a single router, besides default PHB for conventional best-effort services. End-to-end differentiated services are provided by these PHBs and a specific traffic mediator.
In a network providing DiffServ, traffic streams are classified and marked by routers on a progressing path so as to perform a special per-hop transmission. At this time, traffic streams are processed so that traffic control functions, such as complicated classification, marking, policing and shaping, are mainly performed in edges or hosts of the network, and so that input packets are processed depending on contracted services on the basis of marked values within the network. Therefore, the DiffServ mechanism is advantageous in that there is no need to maintain states and information for respective flows in a core portion of the network having a large number of flows. Accordingly, the DiffServ mechanism is advantageous in that the problem of scalability occurring in the IntServ using RSVP can be solved, but it is problematic in that, if the number of users and the amount of traffic flowing into the network increase, a load to be processed by an edge router increases, thus deteriorating the reliability of a QoS guarantee.